1. Field of the Invention
The invention relates to a process for reducing pollutants, particularly nitrogen oxides, in combustion exhaust gases and a device for reducing pollutants.
2. Description of the Related Art
State of the Technology
Processes and devices for reducing pollutants in combustion exhaust gases in a combustion process that takes place with the supply of oxygen are known. For example, in internal combustion engines in motor vehicles, which use a fuel-air mixture that is ignited with the aid of an ignition means, the nitrogen is removed from the oxygen-nitrogen-air mixture (atmosphere) prior to supply into the internal combustion engine, as disclosed in DE-PS 44 04 681. For this purpose, the oxygen-nitrogen-air mixture is guided across a barrier that is impermeable to nitrogen. Consequently, combustion can continue with the supply of atmospheric oxygen removed from the atmospheric air, while the atmospheric nitrogen present in the atmospheric air is not supplied to the combustion process. The formation of nitrogen oxides during the combustion process is prevented, or at least drastically reduced.
Moreover, ceramic components are known that have a membrane comprising an oxygen ion-conducting material. Components of this type are used, for example, as so-called lambda sensors to determine the oxygen content in exhaust gases of combustion processes. It is known that these oxygen ion-conducting membranes have differing oxygen-conducting capabilities at different temperatures and under different pressure conditions.
So-called zeolites are further known from physical chemistry. They are distinguished by a structure having large, internal hollow spaces that are connected to one another by pores of defined size. These pores of defined size can be set in a range of a few tenths of an Angstrom by, for example, interspersed cations that move freely within the crystal grid and can be exchanged in solution. If such zeolites are acted upon by an oxygen-nitrogen-air mixture, due to the steric effect only the molecules whose diameters are smaller than the width of the pore opening reach the interior of the crystal structure. Thus, a sieving effect occurs. In the kinetic effect, certain molecules diffuse in and through the crystal structure faster than others, likewise causing a separating effect. If the oxygen-nitrogen-air mixture is fragmented, the separation of nitrogen and oxygen is based on the equilibrium effect. In this instance, different absorption forces are responsible for the stronger bonding of one component, for example nitrogen, than another component, such as oxygen.